The present invention relates to a cigarette manufacturing machine.
Cigarette manufacturing machines are known to feature a distributor for receiving shredded tobacco from a feed device and feeding it, through a carding unit and drop-down duct, to a withdrawal unit by which the shredded tobacco is withdrawn from the bottom end of the drop-down duct and fed, in the form of a relatively thin layer, on to a conveyor belt. The layer of tobacco on the conveyor belt is then fed to the bottom end of an upfeed duct along which the tobacco particles are normally drawn up by suction and deposited on to the underside of one or more suction type conveyor belts forming part of a unit for producing at least one continuous cigarette rod.
The main requisite of a cigarette manufacturing machine is that the continuous cigarette rod be as homogeneous as possible, which in turn normally depends on the uniformity of the tobacco layer formed on the conveyor belt, and, consequently, on the regularity with which the tobacco is withdrawn from the bottom end of the drop-down duct, and the manner in which it is fed along the duct.
On known cigarette manufacturing machines, the drop-down duct normally presents a substantially rectangular section, with the long side extending perpendicular to the traveling direction of the conveyor belt. In particular, the drop-down duct presents at least one portion with a constant section, and at least one intermediate portion the section of which varies lengthwise along the duct.
Tests have shown such a design of the drop-down duct to present several drawbacks, by virtue of the tobacco fed into the duct remaining substantially unmixed and, more specifically, undergoing no change in density as it drops down the duct, so that any lack of uniformity in the original mass of tobacco is reflected in the tobacco layer formed on the conveyor belt. Moreover, by virtue of the geometry of the drop-down duct, the density of the tobacco supplied tends to vary not only from one section to another, but also within each section, which variation in density is noticeable in direct proportion to the ratio of the length of the long and short sides of the section.